Field of the Invention: Inter-specific hybrid (Prunus salicianaxc3x97P. persica)/Peach and Nectarine Rootstock.
Varietal denomination: cv. P30-135.
Over half of the annual production costs for California peaches involve hand labor for prunning, thinning and harvesting which is done on ladders because of the large size of the trees. It is widely recognized that production costs could be substantially reduced if the size of the trees could be reduced enough to eliminate the need for ladders in the orchard. The benefit of size controlling rootstocks has been clearly demonstrated in apples and revolutionized the apple industries in Europe and the U.S.
The primary factor in limiting the use of size-controlling rootstocks in stone fruit production is the lack of availability of suitable size controlling rootstocks with a wide range of compatibility among cultivars. In particular, there is a tremendous need for size-controlling rootstocks compatible with peach and nectarine.
xe2x80x98P30-135xe2x80x99 is an inter-specific hybrid (Prunus salicianaxc3x97P. persica) rootstock that is graft compatible with peach and nectarine (P. persica) scion cultivars and confers moderate vigor control (approx. 10-20%) to the peach scions. Peach trees grown on this rootstock are productive and require less pruning and have higher leaf calcium content than trees on Standard rootstock (xe2x80x98Nemaguardxe2x80x99).
xe2x80x98P30-135xe2x80x99 is an inter-specific seedling genotype derived from a cross made in 1978 between Prunus salicina (xe2x80x98Frontierxe2x80x99 plum) and Prunus persica (xe2x80x98Flamecrestxe2x80x99 peach) both unpatented. The seed were stratified and germinated in the greenhouse and the seedlings planted in the field in the spring of 1979 at USDA, ARS, Postharvest Quarantine and Genetics Research Unit plots in Fresno, Calif. The plant was subsequently grafted in 1981 at USDA, ARS, Postharvest Quarantine and Genetics Research Unit, in Fresno, Calif. The first propagation trial was done in 1982 in Fresno from cuttings from the original tree. Sixty-six percent of the cuttings grew in this first propagation trial but subsequent propagation trials have resulted in  greater than 80% success. Subsequent propagation occurred in Oakdale, Calif., Parlier Calif., Davis Calif., and Newcastle Calif. New cultivar xe2x80x98P30-135xe2x80x99, in comparison with the parent xe2x80x98Frontierxe2x80x99, is a peach-lumb hybrid and so has intermediate characteristics between typical peach and Japanese plum cultivars. It does not produce fruit and is useful only as a rootstock. The parent xe2x80x98Frontier,xe2x80x99 in contrast, is a fruiting Japanese plub (Prunus salicina) and thus has all the characteristics of typical Japanese plum varieties. All of the above propagules of xe2x80x98P30-135xe2x80x99 were stable and produced plants that were true to type of the initial new cultivar, as shown by statistical data in the Tables. Initial screening for susceptibility to rootknot nematode indicated that xe2x80x98P30-135xe2x80x99 is mildly susceptible.
In November, 1986, cuttings of xe2x80x98P30-135xe2x80x99 were made and planted in a commercial nursery, budded in the nursery in May 1987, and planted at University of California, Kearney Agricultural Center in January 1988. This was a large rootstock evaluation trial involving more that 80 potential peach rootstock genotypes. The peach scion cultivar used in this trial was xe2x80x98O""Henryxe2x80x99. After 7 years of collecting field data in this trial, xe2x80x98P30-135xe2x80x99 was selected for further replicated field productivity trials based on its ease of propagation from cuttings, lack of root suckering, compatibility with peach scions and modest size-controlling characteristics. Crop productivity of the xe2x80x98O""Henryxe2x80x99 scion cultivar grown on xe2x80x98P30-135xe2x80x99 was excellent and comparable to trees on the standard rootstock (xe2x80x98Nemaguardxe2x80x99).
xe2x80x98P30-135xe2x80x99 was propagated again by taking cuttings in November 1994 and planted in a commercial nursery, budded in the nursery in June 1995, and planted at University of California, Kearney Agricultural Center in February 1996. This was a large, replicated field productivity trial involving the eight best potential rootstock genotypes from the 1987 trial. The peach scion cultivars for the main part of this trial were xe2x80x98Flavorcrestxe2x80x99 and xe2x80x98Loadelxe2x80x99. After eight years of collecting tree performance data, xe2x80x98P30-135xe2x80x99 stands out as a rootstock that has modest vigor controlling potential (tree size equal to 90% of trees on the standard industry rootstock, xe2x80x98Nemaguardxe2x80x99) but requires significantly less pruning for light management and would be acceptable for commercial use. Interestingly, leaf calcium concentrations in the scions grown on this rootstock are generally 20-50% greater than on xe2x80x98Nemaguardxe2x80x99.